Ignition timer testing apparatus



Oct. 11, 1949. J, FQUST ETAL 2,484,560

IGNITION TIMER TESTING APPARATUS Filed June 3, 1948 4 Sheets-Sheet l 96 //4 m2 I04- If 9 M 23 I 7 91 I05 1 INVENTORJ 55 M M V 4 Get. 11, 1949. F. J. FOUST ETAL IGNITION TIMER TESTING APPARATUS 4 Shets-Sheet 5 Filed June 3, 1948 Oct. 11, 1949' F. J. FOUST ETAL IGNITION TIMER TESTING APPARATUS 4 Sheets-Sheet 4 Filed June 3, 1948 Patented a. 11, 1949 Floyd J.

Foust, Olven W. Childress, Jr., and Rupert C. Whelchel, Anderson, to General Motors Corporation,

Ind., assignors Detroit, Mich.,

a corporation of Delaware Application June 3, 1948, Serial No. 30,946

. 4 Claims.

This invention relates to equipment for testing spark advance of ignition timers. The object of the invention is to provide a visual indication of spark timing over the range of speeds to which the timer would be subjected in service. The visual trace is on the screen of a cathode ray oscilloscope having one of its plate pairs subjected to a voltage which increases as spark advance increases and having the other pair of its plates connected to a voltage which is proportional to speed. In front of the cathode ray screen there is placed a. card showing the pattern limits for the particular type of ignition timer under test. If the trace on the screen is within those limits, the timer passes inspection.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. 1 is a front elevation of a device for supporting an ignition timer and for causing rotation of its timer cam shaft at various speeds.

Figs. 2 and 3 together constitute a view in the direction of arrow 2 of Fig. 1, certain parts being in vertical longitudinal section.

Fig. 4 is a sectional view on line 4-4 of Fig. 2.

Fig. 5 is a diagrammatic view showing motor control.

Fig. 6 is a view taken on line 6--6 of Fig. 1.

Fig. 7 is a view in the direction of arrow 1 of Fig. 6.

Fig. 8 is a view shown in the direction of arrow 3 of Fig. 6.

Fig. 9 is a view on the line 9-9 of Fig. 1.

Fig. 10 is a view on the line lfl-IO of Fig. 1.

Figs. 11 and 12 are sectional views on the lines and |2-|2 of Fig. 10.

Fig. 13 is a view, partly in section, on line |3-|3 of Fig. 1.

' Fig. 14 is a sectional view on the line |4-l4 of Fig. 13.

Fig. 15 is a wiring diagram'of electric circuits included in the present invention.

Referring to Figs. 1, 2 and 4, a table supports brackets 2| which support screws 22 which provide trunnions for a frame 23 having lugs 24 each for threadedly engaging screws 25 passing through arcuate slots 26 in brackets 2|. By loosening the screws 25, the frame can be tilted to some angle convenient for the operator and secured in the desired positon by tighteningthe screws 25.

As shown in Figs. 1, 2 and 4, the frame 23 provides notched lugs 30, each of the bifurcations of which carries a bearing 3| for a hinge pin 32. The two pins 32 pass through hinge lugs 33 in tegral with a plate 34 upon which an electric motor 35 is mounted. Motor 35 drives a pulley 36 connected by belt .31 with a pulley 38 attached to a shaft 39. The belt 31 is tightened by threading a screw 40 through the frame 23 and against the plate 34 and the screw is locked by nut 4|.

To the frame 23 there is attached a bearing bracket 43 supporting roller bearings 44 for the shaft 39 which carries the pulley 38. A coupling 45 connects the shaft 39 with the shaft 46 of a tachometer D. C. generator 41. The speed of the electric motor is controlled by an electronic controller 50 of Fig. 5 and is' indicated by the 'voltage of the tachometer generator 41. Con

troller 50 is a niodel electronic controller having a handle 5| which, in the vertical position, effects operation of the motor, 35 at very slow speed only sufllcient to facilitate the connection of the shaft of timer T with coupling 93 (Fig. 2). When the handle 5| is moved right to operate switch 52, the motor 35 operates at a medium speed, 300 R. P. M. for example, at which the speed-responsive automatic spark advance mech anism of timer T is about to begin to operate. When the handle 5| is moved left to operate switch 53, the motor 35 accelerates to high speed. When handle 5| is moved to vertical position, the motor 35 decelerates.

The shaft 33 is connected by a key with a hub 6| which screws 62 connect with a non-conducting disc 63 which supports a metal band or ring 64 connected with segments 65 flush with the outer surface 66 of the disc 63. The ring 64 is contacted by a brush 10 (Fig. 6) attached to a brush holder H which a spring 12 urges clockwise about its pivot 13, one end of said spring bearing against the brush holder, the other against a stud 14. Pin 13 and stud 14 are attached to a non-conducting block 15 supported by bracket 16 attached to the frame 23. The segments 65 are successively engaged by a brush 8!! attached to a holder 8|which a spring 32 urges counterclockwise about a pivot pin 83, one end of said spring bearing against the holder 8| and the other against a stud 84. The pin-83 and stud 84 are insulatingly supported by an arm 85 which (Figs. 2 and 6) has an integral annular flange 85 journaled within an opening 8 in plate 88 which is integral with bracket 16. The location of arm 85 relative to shaft 39 is adjustable by providing screws 39 which pass through arcuate slots 30 in the arm 85 and which are threaded into the plate 88.

The shaft 39 supports a cuplike member 9| attached to the shaft by screw 92 and rotating therewith. The cup 9I receives a coupling 93 secured We set screw 94, said coupling havin the proper slot 95 for receiving av tongue in the lower end of the timer shaft 96 which extends down wardly from the timer T indicated in dot-dash lines in Fig. 2.

The shank S of the housing of the timer T is received by a workholder I which is integral with a sleeve IOI which, surrounds a post I02 attached to a tubular part of the frame I03. Rod I02 has a longitudinal groove I04 for receiving a key I05, thereby preventing rotation of the workholder about the rod I02. The workholder I00 is clamped to the rod I02 by a screw I01 to which a hand wheel I08 is attached. The holder I00 receives a bushing I I0 which supports a bushin I II having a conical inner surface I I2 which receives a chuck II3 which is split in opposite directions as indicated by the cuts H4 and H5 (Figs. 2 and 14), thereby providing wedge portions which can be forced down into the conical surface H2 and be caused to grip the shank S of the timer. This wedging action is effected by screwing down a nut II6 threaded on the upper end of the bushing III, said nut being attached to the handle Ill. The bushing II 0 has a flange IIOa resting upon a holder I 00 and it is retained by a ring I attached to the holder by screws IN. The flange II 0a has a notch I22 which receives a pin I23 carried by a handle I24 pivoted on a pin I25.

Referring to Figs. 10, 11 and 12, the holder I00 supports rods I30, each having a reduced portion I3I providing pivotal supports for non-conducting levers I32 and I33 to which rivets I36 attach arcuate metal contacts I34 and I35 respectively for engaging terminals of the timer in case it has two insulated terminals. If it has but one insulated terminal, one of the connectors would engage it and the other would engage the side of the timer which would serve as a ground connection in the insulation of the timer on an engine. The levers I32 and I33 are retained on the rods I by screws I38 threaded into the rods. Levers I32 and I33 provide respectively metal inserts I42 and I43 which serve as lever arms, said arms being connected by a pin I44 passing through a slot in one of the arms. The levers I32 and I33 are connected by a spring I45 whose ends are connected with studs I46 carried by these levers. When the studs I46 are below a center line joining the centers of the screws I38 as viewed in Fig. 10, the spring I45 urges the contactors I34 and I toward each other; and, when the levers I32 and I33 are moved outward so that the studs I46 are above a center line of the centers of the screws I38, the spring I will urge the contactors apart. When the timer T is located for test as shown in Figs. 2 and 10, the levers I32 and I33 are moved manually into the position shown so that the contactors I34 and I35 will engage the timer terminals. After the test, the levers I32 and I33 are manually retracted to an extent such that the spring I45 retains the levers in retracted position. The contactors, when engaging the timer terminals, connect the timer with the test circuit as shown in Fig. 15.

The following lists parts of the circuit (Fig. 15) and specifications which have been found satisfactory.

Cl 16 mfd. 450 volt condenser 02 16 mfd. 450 volt condenser C3 C4 C5 C6 C1 C3 C9 CIO CII CI2 CI3 CI4 CI5 CI6 CI'I CIB HI H2 H3 H4 H5 H6 H1 16 mfd. 450 volt condenser 4,000 mfd. 25 volt condenser 16 mfd. 450 volt condenser 4,000 mfd. 25 volt condenser 50 mfd. 150 volt condenser 16 mfd. 450 volt condenser 16 mfd. 450 volt condenser 16 mfd. 450 volt condenser 16 mfd. 450 volt condenser 4,000 mfd. 25 volt condenser .003 mfd. 2500 volt condenser .003 mfd. 2500 volt condenser 2 mfd. 3,000 volt condenser 2 mfd. 3,000 volt condenser l mfd. 3,000 volt condenser 1 mfd. 3,000 volt condenser 150 milli-amps choke 150 milli-amps choke 8 henrys milli-amps choke 8 henrys 100 milli-amps choke 8 henrys 100 milli-amps 7,000 v. ins. choke 8 henrys 100 milli-amps 7,000 v. ins. choke 100 henrys special 7000 turns (#32 wire) choke 100 henrys special 7,000 choke 0 to 3 milli-ammeter meter 2500 ohms 50 watt resistor 4 ohms 50 watt resistor 25 ohms 20 watt resistor 25 ohms 20 watt resistor 25 ohms 20 watt resistor meter shunt 60 milli-amps 2,000 ohms 10 watt resistor 1,000 ohms 4 watt resistor 2,000 ohms wire wound potentiometer 500 ohms 10 watt resistor 500 ohms 1 watt resistor 25,000 ohms 20 watt resistor 50,000 ohms 25 watt resistor 6,000 ohms 20 watt resistor 100,000 ohms 25 watt resistor 10,000 ohms 20 watt resistor 500 ohms 1 watt resistor 380,000 ohms 10 watt resistor 380,000 ohms 10 watt resistor 380,000 ohms 10 watt resistor 380,000 ohms 10 watt resistor 25,000 ohms 1 watt resistor 100,000 ohms 10 watt resistor 100,000 ohms 10 watt resistor 25,000 ohms 1 watt resistor 25 ohms 25 watt resistor 4,000 ohms 25 watt resistor 25 ohms 25 watt resistor 4,000 ohms 25 watt resistor 2 megohm 2 watt resistor 2 megohm 2 watt resistor 2 megohm 2 watt resistor 2 megohm 2 watt resistor 500,000 ohm 1 watt resistor 1 megohm 2 watt resistor 250,000 ohms 1 watt resistor 500,000 ohms 1 watt resistor 50,000 ohms 50 watt resistor 1 megohm 1 watt resistor 305-B Advance relay 454 type volt A. 0. Advance relay 979-A type 115 volt A. C. Advance relay Normally open micro-switch 800 volts center tap 200 milli-amp. transformer Mallory 5535-3 battery charger 30 volts 2 amp transformer 14 volts 2 amp transformer turns #32 wire) 6.3 volts 1 amp transformer 700 volts center tap transformer 500 VA. voltage regulator 6VA10 Mallory rectopower supply 6VA10 Mallory rectopower supply 5 volts 10 amp transformer 1800 V. C. T. 225 milli-amp transformer 2.5 volts 10 amp transformer 2.5 volts 1 amp transformer T45158 transformer 2.5 volt 1 amp transformer Thermador 088763 83 full wave mercury vapor rectifier OD3 voltage regulator OD3 voltage regulator OD3 voltage regulator 2050 Thyratron 14 APl cathode ray tube Du Mont 811 transmitting triode 811 transmitting triode 811 transmitting triode 811 transmitting triode 6V6 beam power amplifier 6V6 beam power amplifier 6x5 full wave high vacuum rectifier 83 full wave mercury vapor rectifier C3 voltage regulator 0C3 voltage regulator 816 half wave mercury vapor rectifier 816 half wave mercury vapor rectifier 816 half wave mercury vapor rectifier 816 half wave mercury vapor rectifier 2x2 half wave high vacuum rectifier V22 2x2 half wave high vacuum rectifier LI Dialco pilot light #9100 (green) L2 Dialco pilot light #9100 (red) Transformer Tl with rectifier VI, filter comprising chokes HI, H2 and condensers CI, C2, supplies direct current to regulator tubes V2, V3, V4 which supply plate current to tube V through the circuit in heavy lines including switch S2 with its contacts in right positions, the rotating disc 53 with its segments 65 (Fig. 8) engageable with brush 80 and its ring engaged by brush l0. Transformer T4 with rectifier cells 200 provides negative bias for the control grid of tube V5 through the circuit indicated by dashes separated by short transverse lines. The bias by this circuit alone is such that tube V5 will not ionize. The signal by this circuit is controlled by a breaker supply circuit indicated by small :rs on a continuous line and including connections with rectifier cells 20I connected with transformer T2, and connected with the primary winding of transformer TIE, contacts 202, 203 of relay RE3 and the circuit breaker contacts 204 of the tested timer T opened by a timer cam 205 and contacts 2| I, 2I2 of relay RE3. When the contacts 204 open, the timer condenser Ct receives a charge due to voltage impressed by the rectifier 2M and by the energy released by the primary winding of transformer TIE; and, immediately thereafter, the timer condenser Ct discharges through the primary winding of transformer TIG, thereby inducing a voltage in its secondary winding which causes grid bias to be decreased negativeiy so that tube V5 is ionized to make it conducting. The bias value on V5 determined by RI I for coarse adjustment and by R8 for fine adjustment is such that V5 will not ionize or conduct until a positive signal is produced by discharge of condenser Ct when the timer contacts 204 open.

The details of timer T (Figs. 2 and 15) are not T5 T5 T1 T8 T9 TIO TII TI2 TI3 TH TI5 TIE VI V2 V3 V4 V5 V5 V1 V8 V9 VIII VII VIZ VI3 VI4 VI5 VI6 VI'I VIB VI9 V20 VZI shown but it will be understood that its cam 205 is driven by its shaft 95 through a speed responsive device such as shown in Fltrsimmons Patent #1,753,564, issued April 8, 1930, which automate ically changes the angular relation between the cam and the shaft in a manner such that timer contacts 204 are separated by the cam 205 further in advance of engine top-dead-center as the speed increases above a certain medi In Fig. 15, the direction of rotation o cam 205 and disc 53 rotating therewith is clockwise. The housin of timer T is so located by the chuck (Figs. 13 and 14) which can be turned for fine adjustment by lever I24 that, at a medium speed of 300 R. P. M., for example, the cam 205 will be.- gin to separate the contacts 204 just as a segment 65 leaves brush 00 (Fig. 6). Therefore there is a brief instant when tube V5 passes current. This is indicated by the appearance of a flash. on the screen of oscilloscope V5. The chuck supporting the timer housing is adjusted until this flash appears when the speed of the timer shaft is that at which the automatic advance mechanism of the timer begins to function.

When the timer shaft is accelerated'by moving lever 5| (Fig. 5) to left position, the time between the instant of separation of timer contacts 204 and the instant a segment 65 leaves brush increases. Therefore that portion of the total time of engagement of brush 80 with a segment 05 during which contacts 204 are open increases with increase of speed of the timer shaft above medium speed. Consequently the tube V5 passes current for increasing periods during engagement of brush 80 with the segments 65 as speed increases. The increment of time of current passed by tube V5 increases from a very narrow value just as the spark advances mechanism begins to function to wider values or rectangular current waves which are increasingly wider as speed increases. Therefore, the width of the current waves is substantially proportional to spark advance.

Part of the current passed by tube V5 passes to ground through resistances R1 and R8, the latter being adjustable for a fine adjustment for controlling the critical point for ionizing tube V5. This adjustment also limits the height of the wave form so that the beam will be on the screen of the cathode ray oscilloscope. Adjustable resistance R9 controls the amount of D. C. voltage impressed on the grid of the tube VII for amplification thereby and by tubes V|0.and- V9 in the circuit of the plates 220 and HI of oscilloscope V6. The D. C. signal received by plates 220, MI is the average voltage development across R9. Chokes H1 and H8 and condenser C3 provide means for averaging the current flow. The greater the conducting time of tube V5 becomes, the higher the average voltage developed across R9 becomes. Consequently, average voltage amplified and impressed on plates 220, 22I increases as spark advance increases. The relation of the inductances of chokes H1 and H8 to the capacity of C3 must be such that for the varying frequencies encountered over the range of speeds of the time, the cathode ray oscilloscope will show a dot on its screen.

Horizontal plates 222, 229 of the oscilloscope receive voltages proportional to timer shaft speed. Tachometer D. C. generator. 41 is connected with plates 222, 223 through the circuit indicated by continuous lines with dots thereon. This circuit includes a connection with grounded resistance R39 (connected with a terminal of generator 41 value.

timing intervals condenser Ct are unequal.

and with condenser CI2), amplifier tubes VI2 and V8, plates 222, Hand amplifier tube V1 to ground. As the timer speed increases, the output of the D. C. generator 41 increases. 'The circuit including condenser CI2 and resistance R39 provide that the voltage impressed on the plates 222 and 223 through amplifier tubes V8 and V1 shall increase in proportion to speed increase.

Since oscilloscope plates 220, 22I receive voltage signals in proportion to spark advance and plates 222, 223 receive voltage signals in proportion to timer shaft speed, there appears on the oscilloscope screen 224 a trace of the spark advance curve. This trace appears more or less continuous depending on the rate of acceleration of the timer shaft. whether the trace falls in a zone between two limit curves marked on the screen 224. If any part of the trace falls outside the zone, the timer does not pass inspection for spark advance.

The test for spread is to determine the synchronism of sparking. A perfectly synchronized timer should provide sparks at equally spaced intervals. For example, a conventional four cycle, six cylinder engine would require a spark every 120 of crankshaft rotation or every 60 of camshaft rotation. Due to slight variations in manufacture (cam contour for example), the inter- .vals between sparking may vary from 60 slightly.

The timer is serviceable if the variation, is not too great. The variation is called spread.

To test for spread, the timer is rotated at constant speed and the switch SI is closed to connect a current source through connections ww with the magnet coil 2I0 of relay RE'3 and the source with coil 225 of relay RE2. The energization of coil 225 causes relay RE2 to condition the oscilloscope for the spread test, by disconnecting its element 226 from the contact 221 of relay RE2 and connecting said element with contact 228. This makes the intensity of return trace only slightly visible. Only the peak is plainly visible. The energization of coil 2I0 causes relay RE3 to separate contacts 2 and 2I2, contacts 202, 203 and contacts 206, 201 and to engage con tacts 203, 209, contacts 2, 2I3 and contacts 201, 208. Then a spread circuit represented by lines with small circles at one side thereof will be established. This circuit includes a connection with rectifier cells 230 connected with transformer T3, the closed contacts 2 and 2I3 of relay RE3, and the control grid of tube VII. While this circuit is completed, tube VII is biased to draw plate current near midway of the voltage plate current curve. When the timer contacts 204 open, the timer condenser Ct receives a charge from rectifier 230; and, immediately thereafter, the negative voltage stored in condenser Ct is discharged across RI1 which increases negative bias voltage on VII which changes the plate current of VII momentarily.

.When tube VII is receiving this added bias voltage, there appears on the screen 224 a bright spot which is the peak of the wave resulting from the discharge of condenser Ct across resistance RI1. When the timer contacts 204 close the spot disappears because tube VII is now biased where it drives the spot off the screen 224. Resistance R34 is preset by relay RE2 so the trace of spot leaving the screen is not visible. If the intervals between timer contact separation are exactly equal, the spots will coincide. If are not equal, the charges of Therefore the voltages developed across R" are unequal and the The inspector can see contacts 242 of relay REI.

vations on the screen. The distance betweenlowest and highest spots is an indication of spread. If the spread is between certain limit marks on the screen, the timer passes the spread test.

The plates of tubes VII and VI2 receive a voltage from a source including transformer T6, rectifier tube VI4, a filter circuit (chokes H3 and H4 and condensers CIO and C I I) and a voltage regulator tube VIG. The control grid of tube VII receives a fixed bias from a source including transformer T6, rectifier tube VI 3, a filter circuit (resistance BIZ and condensers C8 and C9) and a voltage regulator tube VI5. When the circuit indicated by small circles adjacent lines is closed by relay RE3 and timer contacts 204, tube VII receives added bias which decreases its plate current. When timer contacts separate, the added bias is eliminated and tube VII again draws more plate current. Hence a spot appears on the screen 224 when the timer contacts separate.

Transformer T1 regulates voltage between lines I and 2 to which the primary winding of transformers TI, T2, T3, T4, T5, T6, T1, T8, T9, TIO, TI2, TI3 and TI 5 are connected. Switch SW3 connects a current source volt A. C.) with lines I and 2. Line I is connected with line Ia by a time delay relay REI comprising a thermal switch 240 influenced by a heater 24I connected with lines 2 and I through normally closed After a lapse of time, switch 240 closes to connect coil 243 with lines 2 and I. When coil 243 is energized, contacts 244 and 245 are closed and contacts 242 open. The heater 24I is open circuited; coil 243 is connected with lines I and 2 by contacts 244; and, lines I and Ia are then connected by contacts 245 and the primary coils of transformers TII and TI4 are connected with lines I and 2. The purpose of the time delay is to withhold operation of the apparatus for supplyin amplifier voltage and gun voltage until the tube cathodes have been heated.

The power supply which includes transformer T8 and rectifier cells 250 supplies current through connections are, to the filaments of tubes VII, VIO, V9. The power supply which includes transformer T9 and rectifier cells 25I supplies current through connections YY to the filaments of tubes VI2, V0, V1. Transformer T5 supplies current through connections zz to the filament of tube V5.

The voltage supply for the plates of tubes VIII, V9, V8, V1 includes transformers TIO, TI I, TI2, rectifier tubes VI1, VI8, VIS, V20 and filter circuit including chokes H5, H6 and condensers CI5, CI6.

The gun voltage supply for cathode ray oscilloscope V6 includes transformers TI3, TI4, TI 5 and rectifier tubes V2I V22.

' Lamp L2 burns to indicate closing of switch SW3. Lamp LI burns to indicate that lines I and la have been connected by relay REI.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. Apparatus for testing an ignition timer having a cam, a pair of contacts separated by the cam, a condenser in parallel with the contacts and speed responsive means for obtaining spark advance by advancing the cam angularly relative to the timer driving shaft as speed increases, comprising a thyratron, a voltage source forthe thyratron plate, means for intermittently connecting the voltage source with the plate and comprising a non-conducting disc driven at the speed of the timer drive shaft and having equidistant conducting segments equal in number to the lobes of the timer cam,means for connecting the segments with a terminal of the voltage source and a brush engageable successively with the segments and connected with the thyratron plate, means for adjusting the timer housing to a position such that at the beginning of the spark advancing function, the timer contacts open just as a segment leaves the brush, a source of negative bias voltage connected with the thyratron grid and causing the thyratron to be non-conducting, means responsive to the opening of the timer contacts for so reducing negatively the thyratron grid bias that the thyratron becomes conducting in consequence of which the thyratron conducts current for successive periods increasing in duration as spark advance increases and the current waves passed by the thyratron increase in width, means for averaging the current flow, a resistance element subjected to the averaged current flow, a connection with the resistance element which receives a voltage signal which increases in ma nitude as spark advance increases, signal amplifying means, a cathode ray oscilloscope, one pair of which plates receive the amplified voltage signal, means for impressing upon the other plates of the oscilloscope a voltage signal corresponding to speed of the timer drive shaft, said means comprising a D. C. generator rotating with the timer shaft, resistance-capacitance circuit connected with the generator for passing a voltage signal which increases in magnitude as generator output increases and means for amplifying said signal and passing it to said other pair of plates of the oscilloscope, and means for driving the generator, timer and disc at various speeds whereby the spark advance curve of the timer appears on the screen of the oscilloscope.

2. Apparatus according to claim 1 further characterized by a means responsive to the opening of the timer contacts for reducing negatively thyratron grid bias which comprises a breaker supply circuitincluding the timer contacts, the timer condenser, a timer condenser charging source and the primary winding of a transformer whose secondary is connected in the circuit of the thyratron grid and its biasing source, the opening of the timer contacts causing the timer condenser to receive a charge and then to discharge through the primary winding of the transformer.

3. Apparatus according to claim 1 in which one end of the resistance element is connected with the cathode of the thyratron and in which the means for averaging current includes two impedances connected in series with the thyratron cathode and includes a condenser connected between the impedances and the other end of the resistance element.

4. Apparatus according to claim 1 further characterized by a spread circuit including the timer contacts, the timer condenser, a timer condenser charging source and a resistance which is subjected to condenser discharge when the timer contacts open, a connection between the resistance and the signal amplifying means first mentioned in claim 1, means for eifecting disconnection of the timer contacts and condenser from the breaker supply circuit. and the connection of the same with the spread circuit, and means for conditioning the oscilloscope for rendering more visible on its screen the peak of the wave of timer condenser discharge than other portions of the wave.

FLOYD J. FOUST. OLVEN 'W. CHILDRESS, JR. RUPERT C. WHELCHEL.

REFERENCES CITED UNITED STATES PATENTS Short Mar. 2, 1943 

